Computer disk drives store information on magnetic disks. Typically, the information is stored on each disk in concentric tracks that are divided into sectors. Information is written to and read from a disk by a transducer that is mounted on an actuator arm capable of moving the transducer radially over the disk. Accordingly, the movement of the actuator arm allows the transducer to access different tracks. The disk is rotated by a spindle motor at high speed which allows the transducer to access different sectors on the disk.
A conventional disk drive, generally designated 10, is illustrated in FIG. 1. The disk drive comprises a disk 12 that is rotated by a spin motor 14. The spin motor 14 is mounted to a base plate 16.
The disk drive 10 also includes an actuator arm assembly 18, which includes a transducer 20 (wherein the transducer has both a write head and a read head) mounted to a flexure arm 22. The actuator arm assembly 18 is attached to an actuator arm 24 that can rotate about a bearing assembly 26. A voice coil motor 28 cooperates with the actuator arm 24 and, hence, the actuator arm assembly 18, to move the transducer 20 relative to the disk 12. The spin motor 14, voice coil motor 28 and transducer 20 are coupled to a number of electronic circuits 30 mounted to a printed circuit board 31. The electronic circuits 30 typically include a read channel chip, a microprocessor-based controller and a random access memory (RAM) device.
The disk drive 10 typically includes a plurality of disks 12 and, therefore, a plurality of corresponding actuator arm assemblies 18. However, it is also possible for the disk drive 10 to include a single disk 12 as shown in FIG. 1.
FIG. 2 is a functional block diagram which illustrates a conventional disk drive 10 that is coupled to a host computer 32 via an input/output port 34. The disk drive 10 is used by the host computer 32 as a data storage device. The host 32 delivers data access requests to the disk drive 10 via port 34. In addition, port 34 is used to transfer customer data between the disk drive 10 and the host 32 during read and write operations.
In addition to the components of the disk drive 10 shown and labeled in FIG. 1, FIG. 2 illustrates (in block diagram form) the disk drive's controller 36, read/write channel 38 and interface 40. Conventionally, data is stored on the disk 12 in substantially concentric data storage tracks on its surface. In a magnetic disk drive 10, for example, data is stored in the form of magnetic polarity transitions within each track. Data is “read” from the disk 12 by positioning the transducer 20 (i.e., the read head) above a desired track of the disk 12 and sensing the magnetic polarity transitions stored within the track, as the track moves below the transducer 20. Similarly, data is “written” to the disk 12 by positioning the transducer 20 (i.e., the write head) above a desired track and delivering a write current representative of the desired data to the transducer 20 at an appropriate time.
The actuator arm assembly 18 is a semi-rigid member that acts as a support structure for the transducer 20, holding it above the surface of the disk 12. The actuator arm assembly 18 is coupled at one end to the transducer 20 and at another end to the VCM 28. The VCM 28 is operative for imparting controlled motion to the actuator arm 18 to appropriately position the transducer 20 with respect to the disk 12. The VCM 28 operates in response to a control signal icontrol generated by the controller 36. The controller 36 generates the control signal icontrol in response to, among other things, an access command received from the host computer 32 via the interface 40.
The read/write channel 38 is operative for appropriately processing the data being read from/written to the disk 12. For example, during a read operation, the read/write channel 38 converts an analog read signal generated by the transducer 20 into a digital data signal that can be recognized by the controller 36. The channel 38 is also generally capable of recovering timing information from the analog read signal. During a write operation, the read/write channel 38 converts customer data received from the host 32 into a write current signal that is delivered to the transducer 20 to “write” the customer data to an appropriate portion of the disk 12. The read/write channel 38 is also operative for continually processing data read from servo information stored on the disk 12 and delivering the processed data to the controller 36 for use in, for example, transducer positioning.
FIG. 3 is a top view of a magnetic storage disk 12 illustrating a typical organization of data on the surface of the disk 12. As shown, the disk 12 includes a plurality of concentric data storage tracks 42, which are used for storing data on the disk 12. The data storage tracks 42 are illustrated as center lines on the surface of the disk 12; however, it should be understood that the actual tracks will each occupy a finite width about a corresponding centerline. The data storage disk 12 also includes servo information in the form of a plurality of radially-aligned servo spokes 44 that each cross all of the tracks 42 on the disk 12. The servo information in the servo spokes 44 is read by the transducer 20 during disk drive operation for use in positioning the transducer 20 above a desired track 42 of the disk 12. The portions of the track between servo spokes 44 have traditionally been used to store customer data received from, for example, the host computer 32 and are thus referred to herein as customer data regions 46.
It should be understood that, for ease of illustration, only a small number of tracks 42 and servo spokes 44 have been shown on the surface of the disk 12 of FIG. 3. That is, conventional disk drives include one or more disk surfaces having a considerably larger number of tracks and servo spokes.
During the disk drive manufacturing process, a special piece of equipment known as a servo track writer (STW) is used to write the radially-aligned servo information which forms servo spokes 44. A STW is a very precise piece of equipment that is capable of writing servo information on the disk surface with a high degree of positional accuracy. In general, a STW is a very expensive piece of capital equipment. Thus, it is generally desirable that a STW be used as efficiently as possible during manufacturing operations. Even a small reduction in the amount of data needed to be written by the STW per disk surface can result in a significant cost and time savings.
FIG. 4 depicts, in block diagram form, certain portions of a conventional servo track writer 50 and a disk drive 10. Only those components that are used to position the disk drive's actuator arm assembly 18 radially relative to the center of the disk surface are shown in FIG. 4. Among other things, the servo track writer 50 includes an STW digital signal processor (DSP) 52, a STW voice-coil motor (VCM) 54, a STW actuator arm assembly 56 and a push-pin system 58.
In order to write servo information on to a disk surface 12, the disk drive 10 is loaded onto the STW 50 and is held securely in place. One of a variety of push-pin systems 58 (e.g., a mechanical push-pin system or an optical push-pin system) is used to create an interface between the actuator arm assembly 18 of disk drive 10 and the actuator arm assembly 56 of the servo track writer 50. By properly positioning the STW actuator arm assembly 56, the actuator arm assembly 18 and, hence, the transducer 20 of the disk drive 10 may be positioned at an appropriate location relative to the center of the disk surface 12. In order to effectuate this positioning, the STW 50 uses a servo loop formed by an external relative encoder (see block 70 in FIG. 6), which cooperates with (or forms a part of) the STW VCM 54, and a compensation circuit (see block 70 in FIG. 6).
Once the transducer 20 is appropriately positioned relative to the disk surface 12, servo information is then written by the transducer 20 onto the disk surface 12 at the particular radial location. Subsequently, the STW actuator arm assembly 56 is used to position the actuator arm assembly 18 of the disk drive 10 at a next radial location and servo information is written at this radial location. The process repeats until servo information is written at all predetermined radial locations across the disk surface 12.
As shown in FIG. 4, the STW 50 also includes a crystal 60 and a divide-by-N circuit 62 which are used to provide a series of interrupt signals 64 (see FIG. 5) to the STW DSP 52 at predetermined sample times, Ts. Upon receipt of an interrupt signal 64, the STW DSP 52 performs an interrupt service routine (ISR) 66, which last for a duration generally less than the sample time, Ts, as indicated by the brackets shown in FIG. 5.
FIG. 6 depicts, in block diagram form, the steps of a conventional interrupt service routine. As shown in FIG. 6, the ISR broadly includes the steps of: profile generation (block 68), STW servo loop closure, whereby the generated profile is followed (block 70), and communication/housekeeping between the host computer 32 and the STW DSP 52 (block 72).
Although not shown in FIG. 4, the STW 50 also includes an external clock head assembly and a phase-locked loop (PLL). The external clock head is used for reading a clock track that has been written on the disk surface 12 using conventional techniques. The phase-locked loop (PLL) is provided to maintain very accurate physical transitions relative to the disk surface 12. Importantly, in the conventional STW 50, the transducers 20 of the disk drive 10 are “placed” and “held” at radial positions relative to the center of the disk 12 completely independently from the clock PLL. It is only after the transducers have been “placed” at a radial position that the transducers 20 write the appropriate servo pattern clocked out by the PLL clock via a pattern generator, which keeps track of the circumferential position. After the servo pattern has been written, the transducers 20 are moved to the next radial position (again, independent from the clock PLL) and the process is repeated. Eventually, servo information is written across the entire disk surface to form the servo spokes 44 shown in FIG. 3.
Because servo information is currently written by placing transducers at radial locations across the disk surface and then writing servo information which is used to define a track, the time for writing servo information increases as the total number of tracks able to be placed on a disk surface increases. Since the number of tracks per inch (TPI) continues to increase, manufacturing times are likely to continue to increase, unless more servo track writers are supplied. However, as alluded to above, the purchase of additional servo track writers involves a significant capital expense.
In order to solve this problem and to expedite the manner by which servo information is written onto a disk surface (among other things), it has been determined that it would be beneficial to write servo information in spiral patterns (see, U.S. patent application Ser. No. 09/853,093 filed May 9, 2001 and U.S. patent application Ser. No. 10/126,917 filed Apr. 19, 2002, both of which are incorporated herein by reference in their entireties). FIG. 7 is a simplified diagrammatic representation of first and second spiral patterns 100, 102 written onto a disk surface 12. Each of the spiral patterns 100, 102 is written while the transducer 20 is dynamically moved across the disk surface 12 at a constant or variable velocity. The spiral patterns 100, 102 may include a constant frequency pattern with sync marks (represented by black squares in FIG. 7) imbedded therein. During operation of the disk drive 10 or during a self-servo writing process, the sync marks are used to position a transducer 20 over the disk surface 12 and, hence, forms (at least a part of) either the final or some intermediate servo information.
Writing servo information in such a manner presents a number of new problems. For example, since the transducer 20 is not “placed” and “held” at a particular radius relative to the center of the disk surface 12 before servo information is written, it would be desirable to develop a method for ensuring that corresponding sync marks along different spirals are located along the same radius. Furthermore, it would be desirable to develop a method for ensuring that the circumferential distance between adjacent sync marks along the same radius is equivalent. Reference is made to FIG. 8, which is diagrammatic representation of a fragmentary top view of a disk surface 12 having two spiral patterns written thereon, to illustrate these points.
As shown in FIG. 8, portions of Spiral N and Spiral N+1 are written on disk surface 12. A first sync mark 104 associated with Spiral N is written along Spiral N near the outer diameter of the disk surface 12. Similarly, a first sync mark 106 associated with Spiral N+1 is written along Spiral N+1 near the outer diameter of the disk surface 12. For the servo information to properly perform its function, sync mark X of Spiral N and sync mark X of Spiral N+1 should lie on the same radius R relative to the center 108 of the disk 12. Furthermore, the circumferential distance between adjacent sync marks along the same radius should be the same. For example, the circumferential distance between adjacent sync marks that lie along radius R should be equal to the circumferential distance D between sync mark X of Spiral N and sync mark X of Spiral N+1.
A further problem is that, as mentioned above, servo track writers are extremely expensive instruments. Accordingly, replacing existing servo track writers with new servo track writers that are used to write servo information in spiral patterns would be extremely expensive. Thus, it would be beneficial to develop a method for writing servo information using spiral patterns by minimally modifying existing servo track writers, rather than requiring altogether new servo track writers.
Yet a further problem is that thermal and/or mechanical changes which occur between the time a first spiral pattern is written and the time a last (or even adjacent) spiral pattern is written may cause large discontinuities (or closure errors). Accordingly, it would be beneficial to devise a method of writing spiral patterns which either reduces the closure errors or which predicts the type of closure errors that are likely to occur, so that the disk drive's servo system may compensate for such closure errors.